1. Field of the Invention
The present invention relates to a method of producing double or multiple wall spirally twist tubes. Spiral tubes are normally used for heat exchange applications in which heat is exchanged between a gaseous or fluid medium circulating through the tubes and a second gaseous or fluid medium circulating exterior to the tubes. A leak detector space is provided between the walls of the present invention which can be monitored to detect leakage occurring in the walls prior to the mediums commingling.
2. Description of the Related Art
Several inventions relate to forming single wall twist tubes as revealed by the number of patents included in the accompanying Information Disclosure Statement. U.S. Pat. No. 4,437,329 issued Mar. 20, 1984 to the inventor of the present invention, and which is hereby incorporated in this application by reference, reveals one method of manufacturing twist tubes.
Twist tubes are often used in heat exchange applications because of the increased surface area provided by the twist or convolutions in the tubes. The convolutions increase the surface area of the twist tubes, thus increasing the heat exchange which occurs between either gaseous or fluid medium exterior to the tubes and either gaseous or fluid medium located interior in the tubes.
However, when in use in heat exchange applications, the single wall of an existing twist tube can fail or be breached. When this happens, the medium exterior to the tube and the medium interior in the tube will commingle. Commingling will occur either exterior to the tube or interior in the tube, depending on the relative pressures of the two mediums. Commingling of the mediums is normally undesirable and is particularly undesirable when one medium is a potable water supply, a high purity process stream, or a toxic material.
Need for a double or triple wall twist tube has been identified as evidenced by U.S. Pat. No. 3,730,229 issued on May 1, 1973 and U.S. Pat. No. 3,777,343 issued on Dec. 11, 1973, both issued to inventor Mario L. D'Onofrio. However, both of these patents involve double or triple wall twist tubes which are made by twisting the tubes one at a time instead of twisting all the tubes simultaneously as taught by the present invention. Creation of multiple wall twist tubes utilizing one twisting process instead of multiple twisting processes reduces manufacturing cost, reduces production time, and forms a more unitary twist tube.
The present invention addresses the problem of commingling by providing a double wall twist tube created in one twisting operation which has the desirable heat exchange properties of a single wall twist tube. The present invention is provided with at least two walls to prevent commingling should one wall fail or be breached, and is provided with a leak detector space between its walls to allow monitoring of tube leakage. When one of the walls fails or is breached, medium flows into the leak detector space through the breached wall and travels toward the ends of the tube. The ends can be provided with means for detecting leakage. The means for detecting leakage can be as simple as visually inspecting the ends of the tubes for presence of either of the mediums. When leakage is found, the leaking tube can be either plugged or replaced, thus, preventing the two mediums from commingling.